Different web sites will have different success criteria. Even within a company, different departments might attribute success differently.

For the marketing department, driving more traffic to the site might count as success, even if sales don't increase. For the copywriter, success will come if the content is easy to understand and helps the customer find out more about the company and its products.

For the sales department, increasing the sales conversion per site visitor could be a good measure of success. In summary, there are many ways to measure the success of a site, and all these factors combined will give the truest and most accurate overall measure of success.

Traffic

One of the most obvious measures of success is traffic. The more visitors to the site, the higher the profile, the more people will know about your site, and the more opportunities you have to build a customer relationship. However, if no visitors buy from your site or view more than one page, then traffic alone isn't enough for success...

Sales Ratio

This is how many visitors you need to get one sale. For instance if 1 in 100 visitors purchases from the site, then you have a sales ratio of 1%. One key aspect of success is to try and drive up conversion rates - if selling a product - so that more and more prospects are turned into customers.

Repeat Visits

The more repeat visits you have, the more chance you get to build a customer relationship, build loyalty and ultimately increase sales. Therefore measuring repeat visits is a good measure of success: if people come back and back again then clearly you are fulfilling a need of theirs.

Total Sales

For many people, the total sales is the figure that they look for - how many products were bought through a site in month x? Even though this figure may slightly misguide as to the overall success of a site, it is of course still an important overall measure.